CA2093994A1

CA2093994A1 - Electrically conductive and semi-conductive polymers

Info

Publication number: CA2093994A1
Application number: CA 2093994
Authority: CA
Inventors: Albert C. Chiang; John A. Roderick; Marcelino A. Martins; George B. Martins; Wen-Pin Chen
Original assignee: Individual
Current assignee: Mearthane Products Corp
Priority date: 1992-04-16
Filing date: 1993-04-14
Publication date: 1993-10-17
Also published as: CN1082240A; EP0566418A2; US6361484B1; KR100284640B1; JPH0616948A; AU3692693A; US6063499A; EP0982739A1; US20020077402A1; KR930022392A; EP0566418A3; MX9302237A

Abstract

ELECTRICALLY CONDUCTIVE AND
SEMI-CONDUCTIVE POLYMERS
Abstract of the Disclosure An electrically conductive or semi-conductive polymeric material including a metal salt dissolved in a polymer. The metal salt is complexed with the polymer, which is what provides the material with its conductive properties. The materials have a resistivity of between 105 and 1012 ohms-cm.

Description

~ 1 --ATTORNEY DOCRET NO: 05211/0(12001 Elsctrically Co~duct~e and 8emi-~o~ducti~e Poly~ers Field of the_Invention This invention relates to the field of polymers, 5 particularly urethane rubbers and foams, and to a method of making such polymers electrically conductive or electrically semi-conductive.
Backqround of the Invention In the prior art, polymers, particularly urethane 10 rubber, have been used for a variety of applications in which it is desirable that the product have some electrical conductivity, either throughout the product itself or at least on the exposed surface of the product.
one example involves rollers used in many printers 15 to help transport paper or carry toner in electrograhic printing. The rollers are often made of a polvmer such as polyurethane or covered with a similar polvmer to facilitate their paper-carrying or toner transfer abilityO Different materials, including rubber, may be 20 used in place of polymers for these applications, but because these polymers are much more durable than rubber, they are preferred. Most polymers do not conduct electricity, however, and static charges, which adversely effect the operation of the printer, can build up on the 25 rollers. A similar problem xists if rollers of the same material are used for other purposes, such as carrying semiconductors as part of a semiconductor manufacturing process. Other end uses require conductive or semi-conductive parts as well.
As a result, there have been attempts make such polymer parts electrically conductive. In some cases, the part made from the polymer has been coated with an electrically conductive material. Unfortunately, these coatings have short life spans, and some are toxic.
35 Another approach has been to disperse an electrically-2 IJ ~J 3 ~ 9 ~

conductive material in the polymer when the part is beingfabricated. These electrically-conductive materials have included metal powders such as silver, copper, and nickel, and also materials such as carbon black, 5 graphite, or other conductive polymers. However, the resulting products have several serious drawbacks. In the prior art, in order to make the polymer even semi-conductive, a large amount of conductive filler, eOg., metal powder like carbon black, had to be used, often as 10 high as 10% to 40% of the overall mixture by weight.
This degraded the mechanical and thermal properties of the resulting polymer part. Moreover, because of the size, and nature of the conductive particles, as well as the way in which the particles were mixed with the 15 polymer, conductivity was not very great.
Another related problem is that it is very difficult, due to the relative size and weight of the added particles and the difficulty in dispersing them into the polymeric composition, to achieve a uniform 20 distribution of the conductive material throughout the polymer. As a result of an uneven distribution, the electrical conductivity of the resulting product is not uniform, and the resulting product's mechanical and thermal properties suffer as well. As a result of all 25 this, in general, products made from such compounds have been far less than satisfactory, and in fact, in some applications, become high maintenance items.
Finally, a related problem is that it is often desirable to select the specific conductivity of an 30 polymer in advance, as different end applications preferentially require parts with different conductivities. Selection was not really possible with the prior art methods of making semi-conductive polymers.
Accordingly, one object of the invention is to 35 provide a method by which polymeric materials may be made - 3 ~ 3 3 t~ 9 ~
electrically conductive, without the need for conductive coatings or large amounts of conductive fillers.
Another ob~ect of the invention is to provide a method of making an electrically conductive polymeric 5 material so that the resulting product has uniform electrical conductivity throughout.
Another object of the invention is to provide a method of making an electrically conductive polymeric material so that the relative electrical resistance of 10 the resulting product may be varied with a high degree of accuracy.
Another object of the invention is to provide a method of making an electrically-conductive polymeric material whereby the mechanical and thermal properties of 15 the resulting product are not degraded from what would be expected with a similar material which was non-conductive.
Another object of the invention is to provide a pslymeric material which is electrically conductive and 20 which may be molded and machined.
Another object of the invention is to provide an electrically-conductive polymeric material that is free of voids.
Another object of the invention is to provide an 25 electrically-conductive polymeric material that when used on the surface of rollers, e.g., in a printer, inhibits build-up a static charge on the roller.
Another object of the invention is to provide a polymeric material with good thermal stability.
Summary of the Invention The invention features an electrically conductive or semi-conductive polymeric material that has a resistivity of between 10l2 ohm-cm and 105 ohm-cm. The material i5 a solid solution of metal salt dissolved in a 35 polymer. The metal salt is complexed with the polymer, 2 i3 ~ 3 ~
which is what provides the material with its conductive properties. Depending on the desired resistivity, the quantity of metal salt in the material can be vari~d, although preferably the material includes only a small 5 amount (less than 1%, more preferably less than 0.1%) of the metal salt by weight. B~cause only a small amount of the metal salt is included in the material, the material has good mechanical and thermal propertie~. These properties, coupled with the conductive nature of the 10 material, make the material suitable for use as coatings on, e.g., rollers used on paper printers.
The preferred polymers contain, e.g., nitrogen, oxygen, sulfur or halida atoms, or unsaturated (double and triple bond) groups, which are available for 15 complexing with the metal salt. Preferred polymers include elastomeric polymers like polyurethanes and rubbers, adhesive polymers, and plastics. When rubbers are used, the material also preferably includes a plasticizer.
Preferred metal salts suitable for use in the material include transition metal halides like CuCl2, CuBr2, CoC12, ZnCl2, NiC12, FeCl2, FeBr2, FeBr3, CUI2, FeCl3, FeI3, and FeI2. Other preferred salts include Cu(NO3)2~ copper lactate, copper tartrate, iron phosphate, 25 iron oxalate, LiBF4, and H4Fe~CN)6.
The invention also features a method of preparing these polymeric materials. Generally, the method includes making a homogenous solution of the metal salt in a polymer or polymer precursor, and curing the 30 composition. When the polymer precursor is an isocyanate functional prepolymer, the solution also includes an extender (polyol or polyamine) that reacts with the isocyanate groups during curing to form a polyurethane resin. This method results in an even distribution of 35 the metal salt throughout the polymeric material, which ,~ ~,i tJ

provides the material with uniform conductivity throughout.
The conductive elastomers are suitable for use in a variety of industrial applications to control surface 5 charge and to provide good heat conductivity and expanded life. For example, the poly~ers can be used to coat the belts, shafts, wheels, inserters, and paper handling and copier toner pick-up rollers in paper printers. The polymer can be used to coat car bodies, print circuits, 10 seals, and to dissipate charges in various other electrical applications, such as coating on belts that are used to transport semiconductor wafers during manufacture. The conductive plastic materials (such as nylonl can be used to coat disc drives, machine body 15 parts, cabinets, and carry cases.
Other features and advantages of the invention will be apparent from the description of the preferred embodiment thereof, and from the claims.
Description of the Preferred Embodiment The preferred polymers are polyurethanes. The preferred method of preparing conductive polymeric materials including a polyurethane is to mix an extender (polyol or amine) or an isocyanate-functional prepolymer with a solution of a metal salt. The mixture is then 25 cured. Of course, other standard ingredients, like a cure accelerator or a flame retardant, may be included in the mixture.
Example l - Conductive Laser Roller A steel core was coated with an adhesive (Thixon 30 AP 3437 from Morton International, West Alexandria, Ohio). The part was then completely dried.
A 5~ solution of copper chloride was prepared as follows. In a one liter container, 475 grams of Fyrol PCF (tri(B-chloropropyl) phosphate, available from Akzo 35 Chemical Inc., Chicago, IL), 475 grams of Fyrol CEF

- 6 - 2~,~93~9~
(tri(B-chlorethyl) phosphate, available from Akzo Chemical Inc., Chicago, IL), 50 grams of dried copper chloride (available from Aldrich Chemical Company, Milwaukee, WI), and 6 grams of Pluracol TP-440 (polyol 5 available from BASF Corporation, Parsippany, NJ) were mixed under mechanical stirring at 200-500 rpm and at 220 F for 2 hours. A green solution was obtained.
A 55 gallon resin tank (made by Amplan Inc., Middlesex, NJ, equipped with vacuum, stirring, pressure, 10 venting valves and temperature control) was filled with a polyisocyanate functional prepolymer, Vibrathane 8011 (available from Uniroyal Chemicals, Middlebury, CT) and the temperature raised to, and maintained at, 170F. In a 15 liter container, 8200 grams of Isonol 93 (available 15 from the Upjohn Co., Kalam~zoo, MI), 1400 grams of TIPA
(tributoxyethyl phosphate, available from FMC Corp. of Nitro, WV), 160 grams of copper chloride solution (5~) and 48 grams of Metacure T-12 (dibutylton dilaurate, available fro~ Air Products, Allertown, PA) were mixed 20 with mechanical stirring at 200-500 rpm for 5 minutes at room temperature. The TIPA increases the solubility of the ingredients; the T-12 is a catalyst. The mixture was then degassed for 30 minutes under vacuum. The mixture was transferred to the 5 gallon curative tank (made by 25 Amplan Inc. and equipped with a mechanical mixer~.
Both the prepolymer and the curative were mixed through an Automatic Process Control dispenser to produce a uniform mixing. By adjusting the flow rate for each tank, 148600 grams of the prepolymer (Vibrathane 8011) 30 and 9800 grams of the curative were mixed thoroughly.
The mixture was charged to each casting mold surrounding the steel cores. The mixture then was cured in the casting mold at 260F for 20 minutes. It was then demolded and left in the oven at 230F for 12 hours.

- 7 - ~J939.~-~
The cased roller was then ground to obtain the specified dimensions. The finished part has hardness of 53 Shore A and had electrical resistivity of 3 x 109 ohms-cm.
Example 2 - Conductive Laser Roller A second conductive laser roller was made by an analagous procedure as in Example 1, except that the formulation was changed to the following:
ComponentsWeiqht (qrams) copper Chloride 800 The finished part had a hardness of 53 Shore A and a resistivity of 1.5 x 109 ohms-cm.
Example 3 -- ~on-Foam Polyurethane Formulation and the Effect of Varyina the Quantity of Metal Salt A 0.5% solution of copper chloride (lOg) is added to l90g of Metacure T-12 and mixed until the copper chloride dissolved. The resulting copper chloride solution (165g) was mixed with 8200 grams of polyol-234-630 (polyglycol, available from BASF, NJ), and this 25 solution is mixed with 1300 grams of trisopropanolamine 99 (available from Dow Chemical USA, MO) at room temperature. This solution (30.4g) is then vigorously mixed with 455g of Vibrathane 8011 at 90-110F. The mixture was then poured into multiple cavity molds and 30 cured at 220-250F for 30 minutes. It was demolded and post-cured in an oven at 220F for 12 hours. The urethane rubber had a resultant of 3.5 x 109 ohms-cm.
The amount of copper chloride in the material was O.03%. Further materials were made in which the quantity 35 of copper chloride was increased while the remaining materials remained the same. The resistivity dropped 2 ~

- ~ -tmore conductivity) as the level of copper chloride increased, as follows:
Amount (arams) of CuCl2 per lOOg of polyol Resistivity (ohms-cm~
5.0 x 10-6 4.0 x 101 5.0 x 10-5 3.5 x 109 7 x 10-5 3.0 x 109 9.4 x 10-5 2.1 x 109 1.5 x 10-4 1.7 x 109 2.0 x 10-4 1.2 x 109 3.0 x 10-4 9.0 x 108 5.0 x 10-4 7.0 x 108 9.0 x 10-3 2.0 x 108 1.4 x 10-2 7.6 x 107 1.9 x 10-2 1.8 x 107 2.5 4.4 x 106 5.0 5.0 x 105 Example 4 -- Other Non-Foam Polyurethane Formulations A metal salt solution (25%) was formulated with 15 grams of the metal salt; 20 grams of a flame retardant, tri-(B-chloropropyl)phosphate; 20 grams of Isonol 93; and 5 grams of tributoxyethyl phosphate. The metal salts that were used in the solution included zinc chloride, 25 cobalt chloride, iron oxalate, lithium chloride, copper bromide chromium chloride, and copper chloride, all of which were purchased from Aldrich Chemical Co. of Milwaukee, Wisconsin. The salts were ground and dried prior to use. The solutions were prepared by 30 mechanically mixing ~t 200-500 rpm at 150F for 1-3 hours.
The 25~ metal salt solution (50 grams) was combined with a 38 grams of an extender MOCA (4,4'-diamino-3,3'-dichlorodiphenylmethane, available from 35 Palmer Davis Seikra, Inc., NY), and a polyurethane c~ 3 1 g prepolymer, Vibrathane B-601 (a polyester/TDI prepolymer, available from Uniroyal Chemical). This was done by adding first the MOCA and then the prepolymer to the metal solution, with mixing, at 180-220F. Vigorous 5 mixing continued for 2-5 minutes.
The mixtures were then poured into a multiplecavity metal mold, and the prepolymer was cured at 220-250F for 30 minutes. The material was removed from the mold and post-cured in an oven for 12 to 20 10 hours at 200F, after which curing was completed by letting the material sit at room temperature for at least 3 days to complete curing.
The polymeric materials that were obtained had the following resistivities:
Salt Resistivity (ohms-cm~
zinc chloride2.5 x 101 cobalt chloride1.2 x 1ol0 iron chloride1.0 x 106 iron oxalate 1.3 x 101 lithium chloride1.6 x 101 copper bromide1 x 1o6 chromium chloride 1.9 x 101 copper chlorids5.0 x 1o6 Example 5 -- Polyurethane Foams The following conductive foams were prepared according to the same general procedure used above. The numbers in the table are the grams of the particular ingredient included in the example. The metal salt solutions were prepared as described previously; a foam 30 agent such as methylene chloride, H2O was used. The notes at the end of the table supply further information concerning the ingredients.

- lo - 2~, 3~99~
ExamDle ~
In~redient~ 1 2 3 4 5 6 7 8 p_3801450325 143 155 180180180 400 DC 20021.8 1.8 6.6 10 76.6 7 7 81ack ~48003 6 6 2.33 3.5 5 2.33 5 15 Methylene 6 16 4.33 65 4.33 4.33 4.33 4.33 chloride Water3.53.5 1.3 2.25 1 1 1 0.5 DABCo43.53.5 1.1 0.5 0.51.16 drop drop B-9-885 1 1 0.33 0.5 0.33 0.33 0.33 20 ~--1260.10.1 -- -- -- -- -- --Mondur~ PF7 120 120 56.7 70 50 50 50 53 (22.6%) 35 Metal Salt - 0.5 33.3 25 40 40 40 60 Formula CuC1z CuClz FeClz F~Clz CuClz ~C12 CuCl CuCl Solution 25~ 25~ 25~ 25~ 15~ 20% 20~2 2~

Shoro A 15A 20A 20A 20A 15A 20A loA 30A
40 R~tMq 5xl0l 3xl0 1 ~1o8 sxlo7 5xl07 3~l07 3xl07 ~lO
~OHM~) NOTES
1. P-380 (Pluracol polyol 380) iS a polyether polyol available from BASF Corporation of Wyandotte, Missouri.
2. A silicone surfactant available from Dow Corning.
3. Black #4800 is a black pigment from Pigment Dispersions, Inc.

4. DABC0 is a triethylenediamine catalyst available from Air Products, Inc.

5. B-9-88 (Benzoflex 9-88) is a benzoate ester plasticizer available from Harcros Chemicals Inc.

6. T-12 is Metacure T-12 catalyst.
A further example of a conductive polyurethane foam included 60g of 20% copper chloride solution, prepared as previously described; 3.5g of trimethylolpropane, (available from Celanese Chemical 10 Company of Dallas, Texas); 7g of DC 200; 0.5g of water;
4.3g of methylene chloride; 20g of the B-9-88; and 400g of Vibrathane 8011. The material was prepared by following the same general procedures previously described. The foam had a resistivity of 8 x 106 ohm/cm.
Example 6 -- Semiconductive Rubber Conductive rubber materials are prepared as follows.
Iron Chloride (15g, purchased from Johnson Mathley Electronics of Ward Hill, Massachusetts) are added to 85g 20 of the plasticizer dibutyl phthalate. The mixture is heated to 200C and mechanically stirred for 4 hours. A
dark solution is obtained.
This solution is mixed with rubber materials (such as natural rubber, nitrile rubber, EPDM, styrene 25 hutadiene rubber, neoprene rubber, polysulfide rubber), and polyacrylate rubber, sulfer, and additives for rubber compounding. The rubber was then compression molded at 300psi and 300 F for 20 minutes to cure the rubber.
Example 7 -- Adhesive A copper chloride solution is mixed with a curative and adhesive, such as Thixon 405 (available from Morton International), Chemlok 205, 213, and 214 (available from Lord Corp.), and Conap 1146 (available from Conap Corp~. These adhesives were mixed with copper 35 chloride solutions to provide rubber materials with ~ t J ;j~ '`J (3 4 resistivitieæ of betw~n 1 x 107 ohms-cm and 1 x 1012 ohms-cm. It is then coatad on metal surfaces, dried and casted with urethane rubber~
Example 8 -= Hot Melt Plastic materials are melted and mixed with metal salts under heat. The molten polymer was poured with into mold to form conductive parts, "cure", as used herein, is meant to include this procedure, as well as procedures in which the prepolymer actually cross-links 10 and chemically reacts to form further bonds. The plastic material used should contain electrons donor groups or atoms such as oxygen, nitrogen, sulfur, halides, or unsaturated bonds. The plastic material can be, for example, a polycarbonate, polyimide, polyamide, 15 polysulfer, or fluorocarbon.
Other embodiments are within the following claims.

Claims

1. An electrically conductive or semi-conductive polymeric material, comprising a solid solution of metal salt in polymer, said metal salt being complexed with said polymer to provide said material with a resistivity of between about l012 ohms-cm and 105 ohms cm.

2. The polymeric material of claim 1, wherein said polymeric material comprises less than 5% of said metal salt by weight.

3. The polymeric material of claim 2, wherein said polymeric material comprises less than 0.2% of said metal salt by weight.

4. The polymeric material of claim 1, wherein the molecular size of said metal salt is of between about 1.ANG. and 10.ANG..

5. The polymeric material of claim 1, wherein said polymer is an elastomeric polymer.

6. The polymeric material of claim 1, wherein said polymer is a polyurethane foam.

7. The polymeric material of claim 5, wherein said elastomeric polymer is a polyurethane.

8. The polymeric material of claim 5, wherein said elastomeric polymer is a rubber.

9. The polymeric material of claim 8, wherein said rubber is selected from the group consisting of nitriles, natural rubbers, neoprenes, fluorocarbons, and silicones.

10. The polymeric material of claim 8, said material further comprising a plasticizer.

11. The polymeric material of claim 1, wherein said polymeric material comprises less than 1% of said metal salt by weight.

12. The polymeric material of claim 1, wherein said polymer is an adhesive polymer.

13. The polymeric material of claim 1, wherein said polymer is a plastic, containing electron donating substituents.

14. The polymeric material of claim 1, wherein said material has a resistivity of between about 107 ohms-cm and 109 ohms-cm.

15. The polymeric material of claim 1, wherein said metal salt is a transition metal halide.

16. The polymeric material of claim 1, wherein said metal salt is selected from the group consisting of CuCl2, CuBr2, CoCl2, ZnCl2, NiCl2, FeCl2, Cu(N03)2, FeBr2, LiBF4, and H4Fe(CN)6, CuI2, FeI3, FeCl3, FeBr3, copper lactate, copper tartrate, iron phosphate, and iron oxalate.

17. A roller comprising a cylinder having a surface comprising a conductive or semi-conductive polymeric material comprising a solid solution of a metal salt in a polymer, wherein said metal salt is complexed with said polymer to provide said polymeric material with a resistivity of between about 1012 ohms-cm and 105 ohms-cm.

18. The roller of claim 17 wherein said polymeric material comprises a polyurethane polymer.

19. A method of making an electrically conductive or semi-conductive polymeric material having a resistivity of between 1012 ohms-cm and 105 ohms-cm, said method comprising mixing a metal salt with a polymer or polymer precursor to provide a solution that includes said metal salt and said polymer or polymer precursor;
curing said solution to provide a polymeric material in which said metal salt is complexed to said polymer or a polymer produced from said polymer precursor;
wherein a sufficient quantity of said metal salt is mixed with said polymer of polymer precursor so that the resistivity of said polymeric material is between 1010 ohms-cm and 105 ohms-cm.

20. The method of claim 19 wherein said polymeric material comprises less than 1% of said metal salt by weight.

21. The method of claim 19, wherein said polymer precursor is an isocyanate-functional prepolymer.

22. The method of claim 19, wherein an extender is also mixed with said polymer precursor and said metal salt to provide said curable mixture.

23. The method of claim 19, wherein said extender is a polyol or a polyamine.